1. Field of the Invention
The present invention relates to the preparation of polyisocyanurate foams and laminates. More particularly, the invention relates to the use of a co-catalyst system comprising metal-based and tertiary amine components in the preparation of polyisocyanurate foams from organic polyisocyanates and polyester polyols.
2. Description of the Prior Art
Polyisocyanurate foams are well known and are described, for example, in U.S. Pat. Nos. 3,799,896 and 3,940,517 and in U.K. Pat. No. 1,155,768. Such foams are conventionally made by reacting an organic polyisocyanate with a polyol in the presence of a blowing agent and a catalyst capable of polymerizing isocyanate groups to isocyanurate structures.
One standard, widely accepted, catalyst system used in industry in the preparation of polyol-modified polyisocyanurate foam comprises the combination of 2,4,6-tris-(N,N-dimethylaminomethyl)-phenol known as DMP-30 and potassium 2-ethyl-hexanoate, also known as potassium octoate (see, for example, U.S. Pat. No. 4,169,921). Although this catalyst mixture has proved to be highly useful in many cases, difficulties have been encountered in using it in the preparation of polyisocyanurate foams from polyisocyanates and polyester polyols of relatively high equivalent weight. The resultant foams have been found to be too soft for proper cutting, and the firm time/cream time ratio of the process has been higher than desired for efficient manufacture of the foams on a continuous line. It would be highly desirable if a catalyst system could be found for simply and efficiently manufacturing polyisocyanurate foams of high quality from polyisocyanates and polyester polyols.